When semiconductor devices are manufactured, a process for forming a wiring such as an interconnection line or a contact is carried out. As for this process, a so-called damascene process has been used. In the damascene process, a process for forming a groove or a hole in an interlayer insulating film by etching and burying a metal material in the formed groove or hole is carried out. However, with a recent trend toward miniaturization of a wiring, the damascene process has various problems such as the difficulty of burying a metal material in a fine hole or groove.
In order to deal with the problems of the damascene process, there has been proposed a process for forming a fine copper wiring by forming a copper layer and then etching the copper layer is suggested. This process is disclosed in a document (Fangyu Wu et al., “Low-Temperature Etching of Cu by Hydrogen-Based Plasma”, ACS APPLIED MATERIALS & INTERFACES, 2010, Vol. 2, No. 8, p. 2175-2179). In the process disclosed in the above-cited document, the copper layer is etched by exposing the copper layer to a plasma of a processing gas containing hydrogen gas and argon gas.
The process disclosed in the above-cited document is disadvantageous in that the verticality of a side surface of the copper wiring cannot be ensured in the etching using the plasma of the processing gas containing the hydrogen gas and the argon gas. This problem occurs because an angled portion of a mask may be etched during the etching of the copper layer. In order to solve this problem, a method for etching a copper layer while forming a protective film containing carbon on the mask may be considered.
As described above, the protective film contains carbon and is generally removed by a process using an oxygen plasma. However, the present inventors have found that the protective film is not sufficiently removed in the process using an oxygen plasma.